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        <h1 id="玩转Qml(14)-动画特效-梯度">
            
            玩转Qml(14)-动画特效-梯度
            
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<li><a href="#%E7%AE%80%E4%BB%8B">简介</a></li>
<li><a href="#%E5%85%B3%E4%BA%8E%E6%96%87%E7%AB%A0">关于文章</a></li>
<li><a href="#%E6%A2%AF%E5%BA%A6%E6%95%88%E6%9E%9C%E9%A2%84%E8%A7%88">梯度效果预览</a></li>
<li><a href="#%E5%AE%9E%E7%8E%B0%E5%8E%9F%E7%90%86">实现原理</a></li>
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<h2 id="简介"><a href="#简介" class="headerlink" title="简介"></a>简介</h2><p>这是《Qml特效-进场动画》系列文章的第二篇，涛哥将会教大家一些Qml进场动画相关的知识。</p>
<h2 id="源码"><a href="#源码" class="headerlink" title="源码"></a>源码</h2><p>《玩转Qml》系列文章，配套了一个优秀的开源项目:TaoQuick</p>
<p>github <a href="https://github.com/jaredtao/TaoQuick" target="_blank" rel="noopener">https://github.com/jaredtao/TaoQuick</a></p>
<p>访问不了或者速度太慢，可以用国内的镜像网站gitee</p>
<p><a href="https://gitee.com/jaredtao/TaoQuick" target="_blank" rel="noopener">https://gitee.com/jaredtao/TaoQuick</a></p>
<h2 id="梯度效果预览"><a href="#梯度效果预览" class="headerlink" title="梯度效果预览"></a>梯度效果预览</h2><p>梯度效果，支持从四个方向梯度出现</p>
<p><img src="/images/Animation/2.gif" alt=""></p>
<h2 id="实现原理"><a href="#实现原理" class="headerlink" title="实现原理"></a>实现原理</h2><p>通过数值动画，控制百分比属性percent从0 到100变化</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br></pre></td><td class="code"><pre><span class="line">&#x2F;&#x2F;AGrad.qml</span><br><span class="line">import QtQuick 2.12</span><br><span class="line">import QtQuick.Controls 2.12</span><br><span class="line">ShaderEffect &#123;</span><br><span class="line">    ...</span><br><span class="line">    &#x2F;&#x2F;枚举声明四种方向</span><br><span class="line">    enum Direct &#123;</span><br><span class="line">        FromLeft &#x3D; 0,</span><br><span class="line">        FromRight &#x3D; 1,</span><br><span class="line">        FromTop &#x3D; 2,</span><br><span class="line">        FromBottom &#x3D; 3</span><br><span class="line">    &#125;</span><br><span class="line">    property int dir: ASlowEnter.Direct.FromLeft</span><br><span class="line">    property int percent: 0</span><br><span class="line">    opacity: percent &gt; 0 ? 1 : 0</span><br><span class="line">    NumberAnimation &#123;</span><br><span class="line">        id: animation</span><br><span class="line">        target: r</span><br><span class="line">        property: &quot;percent&quot;</span><br><span class="line">        from: 0</span><br><span class="line">        to: 100</span><br><span class="line">        alwaysRunToEnd: true</span><br><span class="line">        loops: 1</span><br><span class="line">        duration: 1000</span><br><span class="line">    &#125;</span><br><span class="line">    ...</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>在Shader中，使用glsl片段着色器实现像素的控制：</p>
<figure class="highlight glsl"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">in</span> <span class="type">vec2</span> qt_TexCoord0;</span><br><span class="line"><span class="keyword">uniform</span> <span class="type">float</span> qt_Opacity;</span><br><span class="line"><span class="keyword">uniform</span> <span class="type">sampler2D</span> effectSource;</span><br><span class="line"><span class="keyword">uniform</span> <span class="type">int</span> dir;</span><br><span class="line"><span class="keyword">uniform</span> <span class="type">int</span> percent;</span><br><span class="line"><span class="keyword">out</span> <span class="type">vec4</span> fragColor;</span><br><span class="line"><span class="type">void</span> main()</span><br><span class="line">&#123;</span><br><span class="line">    <span class="type">vec4</span> color = <span class="built_in">texture2D</span>(effectSource, qt_TexCoord0);</span><br><span class="line">    <span class="type">float</span> p = <span class="type">float</span>(percent) / <span class="number">100.0</span>f;</span><br><span class="line">    <span class="type">float</span> alpha = <span class="number">1.0</span>f;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">if</span> (dir == <span class="number">0</span> ) &#123;</span><br><span class="line">        alpha = <span class="number">1.0</span> - <span class="built_in">step</span>(p, qt_TexCoord0.x);</span><br><span class="line">    &#125; <span class="keyword">else</span> <span class="keyword">if</span> (dir == <span class="number">1</span>)&#123;</span><br><span class="line">        alpha = <span class="number">1.0</span> - <span class="built_in">step</span>(p, <span class="number">1.0</span> - qt_TexCoord0.x);</span><br><span class="line">    &#125; <span class="keyword">else</span> <span class="keyword">if</span> (dir == <span class="number">2</span>) &#123;</span><br><span class="line">        alpha = <span class="number">1.0</span>f - <span class="built_in">step</span>(p, qt_TexCoord0.y);</span><br><span class="line">    &#125; <span class="keyword">else</span> <span class="keyword">if</span> (dir == <span class="number">3</span>) &#123;</span><br><span class="line">        alpha = <span class="number">1.0</span>f - <span class="built_in">step</span>(p, <span class="number">1.0</span> - qt_TexCoord0.y);</span><br><span class="line">    &#125;</span><br><span class="line">    fragColor = <span class="type">vec4</span>(color.rgb, alpha);</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>效果比较简单，以从左向右为例(dir == 0), 说明一下:</p>
<p>先是把percent 归一化处理 (float p = percent / 100.0)，</p>
<p>纹理坐标qt_TexCoord0.x的取值范围为 0 - 1，按照Qml的坐标系统，左边为0，右边为1。</p>
<p>之后纹理坐标与p进行比较，坐标小于p则显示(透明度为1)，大于p则不显示(透明度为0). (也可以直接用discard丢弃片段)</p>
<p>step是glsl内置函数，step(p, qt_TexCoord0.x) 就是x小于p返回0，大于等于p返回1。 结果正好与上面分析的相反，用1 减去即可： alpha = 1.0 - step(p, qt_TexCoord0.x);</p>
<p>最终输出颜色即可:</p>
<p>fragColor = vec4(color.rgb, alpha);</p>

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